Use function defintion types in header

wiringPi/wiringPi.h

@@ -244,9 +244,12 @@ extern          void digitalWriteByte2   (int value) ;
 // Interrupts
 //	(Also Pi hardware specific)
 
+typedef void isr_function_t();
+typedef void isr_functionx_t();
+
 extern int  waitForInterrupt    (int pin, int mS) ;
-extern int  wiringPiISR         (int pin, int mode, void (*function)(void)) ;
-extern int  wiringPiISRX        (int pin, int mode, void (*function)(void)) ;
+extern int  wiringPiISR         (int pin, int mode, isr_function_t function);
+extern int  wiringPiISRX        (int pin, int mode, isr_functionx_t function);
 
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